In the past folding wheelchairs have commonly been constructed with a seat supported on a framework which has scissor-like bracing permitting the chair to be collapsed so that the vertical sides come towards one another. However, generally such wheelchairs have been heavy and relatively bulky thus presenting problems in loading the wheelchair into a vehicle.
Desirably, a folding wheelchair should be folded readily into a very compact space so that it can be loaded into a small car and furthermore it should be relatively lightweight to permit easy handling of the chair. However, the wheelchair must be strong and durable since wheelchairs are subjected to considerable stresses particularly when the user jumps over gutters or plays sports such as wheelchair basketball. It is also important that a wheelchair can be quickly and easily be folded, for example by a handicapped person after he has transferred himself to the seat of a vehicle.
In this specification the expression "wheelchair" is used not only to cover wheelchairs for invalids but also to cover other forms of wheeled carriages including various forms of baby carriage. Although a major and important application of the present invention is to wheelchairs for invalids and handicapped persons, the invention may also find other applications.
One of the most important design factors for a folding wheelchair is the thickness of the unit when folded. Indeed even a small decrease in the thickness of a folded chair can be extremely valuable in permitting the chair to be loaded into and stored in cars, particularly small cars. Much of the thickness is taken up by main rear wheels which when each rear wheel has a rigid hand rim results in each wheel requiring several inches of thickness. Wheelchairs hitherto available have had, at best, an overall thickness of about 10" when folded and furthermore have had the severe disadvantage of being relatively heavy, for example of the order of 50 lbs. or more.
The present inventor has proposed a useful alternative to wheelchairs hitherto on the market in his U.S. Pat. No. 3,758,150 but it is considered that still further improvements and modifications would be desirable.